The invention relates to an operating device and to a tube lifter which is equipped with an operating device of this kind.
Tube lifters are vacuum handling devices by means of which loads can be grasped, lifted and optionally moved by means of a vacuum. The lifting force is exerted by means of a lifting tube, i.e. a tube that is generally formed in the manner of bellows, is reversibly deformable along its longitudinal extension, can be shortened by applying a vacuum to the tube interior thereof and can be extended again by releasing the vacuum prevailing therein. A suction grip device is generally attached at one end of the lifting tube. The vacuum required for the suction grip device is generally provided by the vacuum prevailing in the lifting tube.
In order to operate the lifting tube, in particular to adjust the vacuum prevailing in the lifting tube, and if required to release said vacuum by a controlled inflow of ambient air, various operating devices are known. The vacuum state in the suction grip device of the tube lifter is generally also controlled by means of the operating devices. Operating devices of this kind generally comprise one or more valve means.
WO 81/02289 A1 discloses a tube lifter comprising a two-step valve means. By actuating a control lever, initially a first valve opening is gradually opened such that ambient air flows into the lifting tube in a controlled manner and the lifting tube can extend. If the control lever is further actuated, an additional ventilation opening is opened such that the lifting tube and the suction grip device are extensively ventilated.
DE 10 2008 028 205 C5 discloses an operating device for tube lifters comprising a handle which has a manually actuable trigger. When the trigger is actuated, first a control valve is opened, by means of which an inflow of ambient air into the lifting tube is controlled. Upon further actuation beyond a pressure point, a second ventilation means is opened, which allows a considerable inflow of ambient air. This additional ventilation of the suction gripper ensures the workpiece is released.
Operating devices of this kind allow intuitive operation, in which first the lifting tube is ventilated and as a result an extension of the lifting tube is initiated under the action of the gravitational force of the load. Only when the corresponding control element is further actuated is complete ventilation carried out, which allows the suctioned object to be released. However, in the ventilated state the lifting tube can no longer be shortened and extended in a controlled manner, but rather remains initially in its extended state.
WO 2007 094 720 A1 describes a tube lifter comprising an operating device which has the features of the preamble of claim 1. A control valve for admitting ambient air into the lifting tube is controlled by means of an operating slide on the handle. Moreover, a separate lever is provided, by means of which a ventilation valve can be opened. The control valve is actuable independently of the remaining valves. The lifting tube and the suction grip device can be extensively ventilated by actuating the lever.
In the known devices, additional ventilation through the ventilation valve can lead to undesired changes in length of the lifting tube. This is problematic in particular if a suctioned object is intended to be released and the lifting tube simultaneously changes its length. As a result, the placed workpiece can tilt or slip, for example.
Moreover, there is a risk that rapid ventilation may cause the suction grip device and the held load to be lowered too quickly. It cannot be ruled out that, in an extreme case, the load is unintentionally released by full actuation of the control element. In particular, if a load has been held at a great height, damage to the load may occur and/or bystanders may be injured.